Apparatus for sharpening rotating blades

ABSTRACT

A sharpening apparatus for a rotating blade is configured such that a rod-shaped grinding tool or a conical cutting-edge surface is movable in the transverse direction. This carried out by a parallelogram linkage. The grinding tool is pressed by a weight under constant contact pressure against the front cutting surface.

RELATED APPLICATIONS

This application claims priority to German Application No. 10 2013 013498.6 filed Aug. 16, 2013, the contents of which are incorporated hereinby reference.

TECHNICAL FIELD

The invention relates to an apparatus for sharpening rotating bladeswhich have a cutting edge running in the circumferential direction.

BACKGROUND OF THE INVENTION

Blades of this kind are used, for example, in machines for slicingproduct loaves, which are also called slicers. The cutting edge of therotating blades is not concentric with the blade axis, but rather hasthe shape of an eccentric circle or a spiral.

When the cutting edge is worn, it must be reground in a sharpeningapparatus. This grinding apparatus has a grinding head which, in knownmachines, is adjusted radially according to the geometry of the cuttingedge (radially with respect to the blade axis).

The different sections of the cutting edge have markedly differentdistances from the axis of the rotating blade, and accordingly a devicefor adjusting the grinding head must be constructed with a correspondingsize.

SUMMARY OF THE INVENTION

An apparatus for sharpening rotating blades which is distinguished by acompact construction is to be specified by the present invention.

This object may be achieved by a sharpening apparatus for sharpeningrotating blades which have a cutting edge running in the circumferentialdirection and bounded by a rear cutting-edge surface and a front conicalcutting-edge surface running in a manner inclined with respect to therear cutting-edge surface having a blade carrying part, to which arotating blade can be fastened and by which the rotating blade isrotated, and a grinding head for regrinding the front conicalcutting-edge surface, which has a rotating cutting tool. The relativeposition between a cutting head or a grinding head with respect to therotating blade is chosen such that the location of engagement betweenthe rotating cutting tool and rotating blade travels in a direction ofan axis of the grinding tool on its lateral surface in dependence on theangular position of the rotating blade.

The sharpening apparatus according to the invention has small dimensionsbecause the change in the position of the cutting edge is accommodatedby the fact that the grinding tool, which is inclined according to thesetting angle of the conical front cutting-edge surface, is movedaxially with respect to the blade axis. Thus, the area of engagement ofthe cutting edge with the grinding tool travels on the lateral surfaceof the latter in the axial direction. The adjusting distance of thegrinding head required for this can be small because the movement of thegrinding tool upon small movements of the grinding tool axis can evencope with large radial differences in the position of the cutting edge,since the angle between the rear cutting-edge surface and a surface lineof the front cutting-edge surface is small, and typically lies in therange from 15 to 25°.

According to one aspect of the invention, it is ensured by structuralfeatures that the grinding tool is moved in the desired presetdirection.

According to another aspect of the invention, the sharpening apparatusis of small construction. The reduction of the cutting speed, causedthereby, compared with conventional grinding discs with a large radiuscan be compensated by increasing the rotational speed of the drive forthe grinding work.

According to another aspect of the invention, movement of the grindinghead is achieved in the axial direction of the grinding tool in themanner of a cam gear can be directly derived from the shape of thecutting edge of the blade. The force with which the tool lies againstthe cutting-edge surface to be reground is always the same. As a result,all regions of the conical cutting-edge surface are reground equally.

According to another aspect of the invention, simple and reliablepossibilities of how the contact pressure of the grinding tool againstthe cutting surface is kept constant may be provided.

According to yet another aspect of the invention, the orientation of therotating blade and of the grinding head during the grinding operationcan be chosen in a manner that is favourable as regards small spacerequirement and ergonomic mounting and demounting of the rotating bladeon the sharpening apparatus. A deflection of the weight, which thusbecomes necessary, is obtained with simple and reliable means.

According to a further aspect of the invention, the transmission of theprestressing force to the grinding tool is also carried out simply andreliably.

According to another aspect of the invention, a linear guidedistinguished by particularly simple and reliable mechanicalconstruction may be provided. Those cooperating surfaces which providethe guidance are small and environmentally sealed, so that impuritiesare kept away from the guide surfaces.

According to another aspect of the invention, the grinding tool mayremain in the immediate vicinity of the cutting-edge surface also insuch angular positions in which the rotating blade has a cutout.

The cutting edge of a rotating blade to be resharpened is preset, on theone hand, by the conical front cutting-edge surface already mentionedabove and, on the other hand, by a rear cutting-edge surface which canlie in a plane transverse to the blade axis, but can also form with thisplane an angle of a few degrees (e.g. about 3 degrees) in bothdirections. The rear cutting-edge surface can be reground with asharpening apparatus together with the conical front cutting-edgesurface.

According to another aspect of the invention, it is ensured that thegrinding tool is always supported by the rotating blade, also in thoseregions of a spiral blade which is free from a cutting edge and wherethe cutting edge jumps back again to a small distance from the axis ofrotation.

In an advantageous aspect of the invention, the grinding tool passesover the connecting edge substantially parallel to this edge.

Other advantages and aspects of the present invention will becomeapparent upon reading the following description of the drawings anddetailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail below using exemplaryembodiments with reference to the drawing, in which:

FIG. 1 shows an axial view of a sharpening apparatus for a spiral bladehaving grinding heads for the two cutting-edge surfaces of the cuttingedge;

FIG. 2 shows a plan view of the sharpening apparatus shown in FIG. 1;

FIG. 3 shows a similar view to FIG. 1, with the rotating blade beingshown in a position rotated by about 60° anticlockwise with respect toFIG. 1;

FIG. 4 shows a plan view of the sharpening apparatus in the positionshown in FIG. 3; and

FIG. 5 shows a similar view to FIGS. 1 and 3, but with the rotatingblade now being shown in a position which is reached shortly after thebeginning of a new revolution of the rotating blade.

DETAILED DESCRIPTION OF THE INVENTION

While this invention is susceptible to embodiments in many differentforms, there is described in detail herein, preferred embodiments of theinvention with the understanding that the present disclosures are to beconsidered as exemplifications of the principles of the invention andare not intended to limit the broad aspects of the invention to theembodiments illustrated.

In FIG. 1, a sharpening apparatus is designated as a whole by 10, whichapparatus serves for sharpening the cutting edge of a spiral bladedesignated as a whole by 12.

The sharpening apparatus has a base plate 14, in which a blade carrier16 is mounted rotatably about a horizontal axis, e.g. by ball bearings(not shown specifically). Acting on the blade carrier 16 is a drivemotor 18, which preferably comprises a geared motor, here a belt drive19.

As can be seen from FIG. 1, the blade has a circular cutout 20 which canreceive the blade carrier 16 in a positive-locking manner. The spiralblade has in the vicinity of the cutout 20 a multiplicity of openings 22which are aligned with threaded bores in an outer flange of the bladecarrier 16, and the spiral blade 12 is connected to the blade carrier 16in a rotationally locked manner by screws (not shown), which are screwedthrough the openings 22.

24 designates a cutting edge in the drawing. In the exemplary embodimentaccording to FIGS. 1 and 2, it runs in the shape of a spiral. Thecutting edge 24 is bounded by a front conical cutting-edge surface 26and a rear plane cutting-edge surface 28 which is perpendicular to theblade axis. The basic shape of the spiral blade 12, in particular itsthickness, is chosen such that the cutting-edge surfaces 26 and 28 arelimited to an outer annular region of the spiral blade 12.

The rear cutting-edge surface 28 can also be the shape of a truncatedcone with a very large opening angle (e.g. 174 degrees), the vertex ofwhich points forwards, or a truncated cone with a very large openingangle (e.g. 179 degrees), the vertex of which points rearwards.

In the spiral blade shown in the figures, a radially outer rear end ofthe spiral blade 12 and a, in the direction of rotation, front radiallyinner end of the spiral are connected to one another by a secant-shapedconnecting section 30. Other geometries of the connecting section arealso frequent, particularly when the total angular extent of the cuttingedge 24 is greater than in the exemplary embodiment shown. Theconnecting section 30 can then also have the shape of an asymmetrical V.

In the claims and the present description, “conical” is to be understoodin connection with the front cutting-edge surface 26 as a surface whosesurface lines encloses an angle to a transverse plane which lies inpractice between 15 and 25°, in the exemplary embodiment considered hereabout 17°. This conical surface is additionally curved in thecircumferential direction.

In connection with the rear cutting-edge surface 28, the angle mentionedcan be between 0 degrees and a few degrees, e.g. about 3 degrees.

The conical cutting-edge surface 26 can, in the case of a genuineeccentric blade (circular blade which is mounted off-centre), haveexactly the shape of a conical surface. It can, however, as in the caseof the spiral blade shown, also have the shape of a conical surfacewhose circumferential curvature changes in the circumferentialdirection.

To sharpen the cutting edge 24, both the front cutting-edge surface 26and the rear cutting-edge surface 28 are reground. This is carried outby a first grinding head 32 and a second grinding head 34, respectively.

The first grinding head 32 has a rod-shaped grinding tool 36 and isdriven by an electric motor 38.

The electric motor 38 is seated on a parallelogram linkage, designatedas a whole by 40. This linkage has a first link 42, which is pivotablymounted at a free, in FIG. 2 upper, end section 44 on a support 46 fixedto the frame.

The support 46 has at its free end a pivotable axial rotary bearing 48for an adjusting spindle 50, the thread of which runs in an adjustingnut 52, which is pivotably supported by a lower section of the link 42.

By rotation of the adjusting spindle 50, the angle between the link 42and the support 46 can thus be adjusted. As a result, the setting angleof the cutting-edge surface 26 is preset.

The link 42 carries, at a place which is spaced about a third of thetotal length from an end bearing 44, a first bearing 56 of theparallelogram linkage 40. A second bearing 58 is situated at the lowerend of the link 42. The second bearing 58 supports one end, located onthe left in the drawing, of a second link 60 of the parallelogramlinkage 40. This link carries, at its end located on the right in FIG.1, a third bearing 62. This bearing is connected to one end of a thirdlink 64, which has at the other end a fourth bearing 66. The latter isconnected via a fourth link 68, the second end of which is articulatelyconnected to the bearing 56.

The four links all have the same length and thus form a parallelogramlinkage. The third link 64 is always parallel to the first link 42. Thesame applies to the links 68 and 60.

The drive motor 38 is fastened at the centre of the third link 64 suchthat the axis of the grinding tool 36 is perpendicular to the link 64.

A rope pulley 72 is connected in a rotationally fixed manner to thefourth link 68 by means of pins 70. Over this pulley runs a rope 74 (notshown in FIG. 2) which is deflected vertically via a deflection roller76. At the lower end of the rope 74 hangs a first weight 78, as can beseen from FIG. 1.

For the second grinding head 34, a second parallelogram linkage 80 isprovided. This linkage comprises a support 82 which is perpendicular tothe base plate 14 and corresponds to the support 46. The links 84, 86,88, 90 and bearings 92, 94, 96, 98 therebetween are the components ofthe parallelogram linkage 80.

The centre of the link 88 carries the second grinding head 34. Thecentre of the link 88 thus carries the drive motor 98 of this head andthe grinding tool 100 driven by it.

The link 96 is connected via pins 102 again to a rope pulley 104, overwhich a rope 106 runs (not shown in FIG. 2). A deflection roller 108deflects the rope 106 in the vertical direction, and its lower endcarries a weight 110, as shown in FIG. 1.

By the mechanism just described, it is ensured that the grinding tool100 bears against the cutting-edge surface 28 always under a constantforce. Again it is the case that the area of engagement between grindingtool and blade disc travels in the axial direction of the grinding toolwhen the rotating blade 12 rotates during sharpening. Again it is thecase that the grinding tool 100 is supported by the rotating blade 12 inall angular positions of the latter.

FIGS. 3 to 5 show the sharpening apparatus in a different angularposition of the rotating blade 12. It can be seen that there is contactbetween both grinding tools 36 and 100, respectively, and the rotatingblade 12 in all angular positions of the rotating blade.

From FIG. 5 it can further be seen that the connecting edge 30 of therotating blade 12 runs parallel to the axis of the tool 36 in a positionclosely adjacent to the grinding tool 36. This means that the grindingtool 36 passes over the connecting edge 30 only with a smallinclination.

Typically, spiral blades and eccentric blades, as used in slicers, havea maximum radius of 20 to 40 cm. The radial dimension of the cuttingsurfaces 26 and 28 is in practice about 20 mm. An outermost section ofthe conical cutting-edge surface 26 can be set a little steeper, asshown in FIG. 2 at 26*. Of course, with such rotating blades theadjusting spindle 50 is then inclined such that the axis of the grindingtool 36 is parallel to the more steeply set, radially outermost partialsurface of the cutting-edge surface 26.

Typically, the pressure with which the grinding tools 36, 100 arepressed against the cutting-edge surfaces 26, 28 is about 50 to about100 p.

From the above description and the drawing, it can be clearly seen thatthe sharpening apparatus has compact dimensions overall. The totaldimension of the sharpening apparatus in the vertical direction in FIG.1 corresponds substantially to the main dimensions of the rotating blade12, as can be seen from FIG. 1.

Instead of a weight, it is also possible to use a pneumatic cylinderconnected to a constant pressure source to prestress the grinding tools36, 100 against the cutting-edge surfaces 26, 28.

While in the foregoing there has been set forth various embodiments ofthe invention, it is to be understood that the present invention may beembodied in other specific forms without departing from the spirit orcentral characteristics thereof. The present embodiments, therefore, areto be considered in all respects as illustrative and not restrictive,and the invention is not to be limited to the details given herein.While specific embodiments have been illustrated and described, numerousmodifications come to mind without significantly departing from thecharacteristics of the invention and the scope of protection is onlylimited by the scope of the accompanying claims.

1. An apparatus for sharpening rotating blades which have a cutting edgerunning in the circumferential direction and bounded by a rearcutting-edge surface and a front conical cutting-edge surface running ina manner inclined with respect to the rear cutting-edge surface,comprising: a blade carrying part, to which a rotating blade can befastened and by which the rotating blade is rotated; a grinding head forregrinding the front conical cutting-edge surface, which has a rotatingcutting tool, wherein the relative position between the grinding headwith respect to the rotating blade is chosen such that the location ofengagement between the rotating cutting tool and rotating blade travelsin a direction of an axis of the grinding tool on its lateral surface independence on the angular position of the rotating blade.
 2. Theapparatus for sharpening rotating blades according to claim 1, whereinthe relative position of the grinding head and the rotating blade ispreset by a linear guide.
 3. The apparatus for sharpening rotatingblades according to claim 1 wherein the diameter of the grinding tool issmall compared with its axial dimension.
 4. The apparatus for sharpeningrotating blades according to claim 1, wherein the grinding head isconnected to a prestressing device, in such a manner that the grindingtool is pressed with constant force against the front cutting-edgesurface.
 5. The apparatus for sharpening rotating blades according toclaim 4, wherein the prestressing device comprises a weight or an aircylinder.
 6. The apparatus for sharpening rotating blades according toclaim 5, wherein the weight is connected to the grinding head via a ropepull.
 7. The apparatus for sharpening rotating blades according to claim6, wherein the rope pull runs over a deflection pulley which cooperateswith a driven part of the linear guide.
 8. The apparatus for sharpeningrotating blades according to claim 2, wherein the linear guide comprisesa parallelogram linkage.
 9. The apparatus for sharpening rotating bladesaccording to claim 7, wherein at least one of the ends of the adjustingpath of the parallelogram linkage is limited by a stop.
 10. Theapparatus for sharpening rotating blades according to claim 1, wherein asecond grinding head is provided, which regrinds the rear cutting-edgesurface and is oriented and/or mounted as described in claim 1 for thatgrinding head which regrinds the front cutting-edge surface.
 11. Theapparatus for sharpening rotating blades according to claim 1, whereinthe movement of the grinding head, the diameter of the grinding tool,the length of the grinding tool and the geometry of the rotating bladeare coordinated with one another such that the grinding tool issupported in every angular position of the rotating blade by therotating blade.
 12. apparatus for sharpening rotating blades accordingto claim 1, wherein the movement of the grinding head, the diameter ofthe grinding tool, the length of the grinding tool and the geometry ofthe rotating blade are coordinated with one another such that in thecase of a spiral blade the axis of the grinding tool is oriented suchthat it is substantially parallel to the main direction of extension ofthe connecting edge when the latter is in the proximity of the grindinghead.